Earlier methods of determining the diameter or circumference of a cigarette filter plug have utilized an air gauge device which requires that the plug be encircled by a pressurized annulus which is arranged to measure the amount of air escaping from the annular gap between the outer circumference of the filter plug and the inner diameter of the annulus. Such a device is operable as long as the circumference wrap of the filter plug is airtight. Such an arrangement permits pressure to build up due to the narrowness of the annular gap between the encircling annulus and the filter rod. If air is permitted to escape via means other than the gap, the measuring system is not accurate. This is the case when the paper forming the outer surface of the filter rod is porous. With the advent and need for a porous outer wrap for the filter plug rather than the relatively airtight wrap used in earlier versions of the filter plug, improved means of measuring the diameter of the filter plug are required. These means must be unaffected by porosity of the filter plug wrapping paper.
In the manufacture of cigarette filter plugs, it becomes necessary to assure that the diameter or circumference of the wrapped plug conforms to the dimensions of the subsequent cigarette resulting from the assembly of the filter plug with the cigarette.
In our copending U.S. patent application Ser. No. 409,754, filed Aug. 19, 1982, we disclosed a process of measuring the circumference of the filter plug in which two or more lines running in a direction parallel to the long dimension of the paper are imprinted on the filter wrap paper. Since the paper is wrapped around the filter plug core fibers so that the long aspect of the paper runs parallel with the filter plug axis, these lines then run longitudinally along the filter rod. By positioning the lines so that they fall near the overlap where the seam is made in the filter rod wrapper as it surrounds the core fiber bundle, means are offered to reference a dimensional measuring system. By determining the separation of the lines positioned on either side of the overlapped seam it is possible to determine the circumference of the filter rod, since the lines are placed a known distance apart and the circumference is composed of this known distance plus the measured distance between the lines as they appear separated by the overlapped seam. Through the use of video measuring apparatus such as a standard television camera or a linear array solid-state video measuring device, the spacing between the two lines separated by the seam can be accurately determined. If four lines are imprinted, the measurement between the outer lines and the inner lines can be used to determine the extent of stretching of the paper thereby offering a means of accurately compensating for the stretch of the paper in the measurement of the filter rod circumference. Should electronic means not be acceptable, an optical measuring device consisting of either a magnifying lens with incorporated reticle or a projection screen device incorporating a scale for measurement may be used.
We have since discovered that a greater simplification may be achieved in the printing of the dimensional establishing elements on the filter wrap material. This simplification is such that only one band of contrasting color or black may be printed on the wrapping material. The result of this discovery is that the production process is simplified for making the gravure roll required to print the wrapper by the gravure process, or making plates or letterpress type to print the wrapper by either the lithographic or letterpress process may be simplified. The nature of our discovery is such that it was unanticipated in our previous disclosure. In our copending process, which was devised around the concept of printing two lines of identical width but spaced to be equidistant from the edges of the filter wrapping material, the process required that the two color stripes or bands be precisely positioned and spaced on the wrapper material. Control of both the width of each band and the spacing between bands must be precise, and this is made difficult by the tendency of the inks used in the gravure process to spread, and the tendency of letterpress and lithographic inks to form an indistinct edge. In the process of the present invention, we provide an improvement in precision because of the eliminations of three printed edges and the necessity for spacing two bands a specified distance apart.